A diesel engine may be started while the engine is at operating temperature, while the engine is near ambient temperature, or while the engine is between ambient and operating temperature. If the diesel engine is started at a temperature that may range from ambient temperature to engine operating temperature, glow plugs may be activated to help initiate combustion within the engine and promote engine combustion stability. Activating the glow plugs may improve engine starting, but it may still be difficult to start the engine due to properties of the fuel being injected to the engine. One fuel property that may vary depending on source of the fuel, regulatory and legislative mandates, location, and time of year is the fuel's cetane number. Higher cetane fuels may tend to ignite earlier or sooner after being injected than lower cetane fuels, and this attribute may make higher cetane fuels more desirable during some operating conditions. However, higher cetane fuels may make engine starting more difficult at low ambient and engine temperatures for engines that are calibrated to the entire spectrum of market available fuel cetane. Nevertheless, a vehicle operator may not have a choice of using a fuel with a cetane number that ideally matches engine operating conditions. Therefore, it may be desirable to provide a way of operating an engine such that the engine may perform as desired whether the fuel injected to the engine is a high cetane fuel or a low cetane fuel.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine operating method, comprising: receiving sensor data to a controller; and adjusting start of fuel injection timing for a cylinder cycle of a subsequent engine start that is responsive to an indication of reverse engine rotation generated via the received sensor data before the subsequent engine start.
By adjusting start of fuel injection timing in response to reverse engine rotation, engine deceleration during engine cranking, or slow run-up speed, it may be possible to operate an engine with different fuels having different cetane numbers or levels during cold engine starting conditions. Further, by balancing a total actual number of pilot fuel injections and/or shifting quantities of fuel injected during pilot and main fuel injections, operation of an engine with fuel that has a higher or lower cetane number may be improved during engine cold starting. In particular, reverse engine rotation or engine acceleration during engine run-up that is less than a threshold engine acceleration rate may be indicative of injecting a higher cetane fuel into an engine during cranking. The engine may rotate in a reverse direction after an engine starter has been disengaged and the engine has failed to accelerate to idle speed because higher cetane fuel may begin to combust in the engine before cylinders of the engine reach top-dead-center combustion stroke. The early onset of combustion may slow down engine speed acceleration or it may decelerate the engine via a combustion related pressure rise in an engine cylinder as the cylinder's piston approaches top-dead-center compression stroke. The cylinder pressure may operate against torque provided via the engine's starter to slow the engine. The engine's reverse rotation may be an indication of high cetane fuel because the higher cetane fuel may ignite early. The start of fuel injection timing may be retarded in response to reverse engine rotation so that combustion may be delayed in the engine, thereby allowing combustion gases to accelerate the engine in a forward rotational direction. Thus, by retarding start of fuel injection timing, engine torque to accelerate the engine during engine cranking may be increased to improve engine starting.
The present description may provide several advantages. In particular, the approach may improve engine starting. In addition, the approach may decrease fuel consumption during engine starting via operating the engine more efficiently. Further, the approach may reduce engine emissions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.